Study On Feedback Phase Compensation Strategy Of LCL Grid-connected Interface Circuit

LCL type grid-connected interface converter is an important interface for connecting power grid and distributed power generation,which equipped as energy management and grid-connected power quality control.In this paper,the three-phase two-level LCL grid-connected inverter is the research object.In order to improve the stability margin under the inverter side current feedback control(CCF),a high frequency phase compensation algorithm(HFPC)is studied.Firstly,the characteristics of the grid-connected interface circuit are analyzed.The state space method and impedance analysis method are implemented to analyze the grid-connected interface in detail.Considering the digital control delay,the state space model and impedance model of the grid-connected system were established.The state space model was used to analyze the operation characteristics under different state feedback,and the output impedance model of the system was established to obtain its anti-interference performance.The grid impedance fluctuation may reduce the system stable margin,so the grid voltage feedforward control is used to improve the anti-interference ability of the grid connected system.Secondly,magnetic particle core inductors are widely used in power inductors because of their high saturation density and low loss characteristics.However,the nonlinear change of inductance also affects the system stable margin.Based on the nonlinear characteristics of the magnetic powder core inductor,the mathematical model of the nonlinear inductor is derived,and the equivalent output impedance model of the magnetic powder core inductor is established.The influence of the nonlinear characteristics of soft magnetic inductance on the system output power quality is studied by theoretical and simulation analysis.To improve the system adaptability for nonlinear characteristics caused by soft magnetic inductance,the phase compensation methods are studied.The linear predictor(LP)based compensation method and its limitations are analyzed by theoretical research and simulation experiments,and a high frequency phase compensation algorithm(HFPC)to improve the phase compensation bandwidth is studied.HFPC consists of improved phase compensation(IPC)and current reconstruction(CR).IPC is used to improve the performance of LP,and CR can improve the current waveform and improve power quality.The validity of HFPC was analyzed by state space method and impedance analysis method,and it was proved that HFPC could not only improve the stability margin of the system,but also enhance the anti-interference ability of the system.In this paper,the feasibility and effectiveness of the research content and the proposed method are verified by simulation and experiment platform.The results show that HPFC can effectively improve the stability margin and anti-interference ability of the system.